Postage metering systems have been developed which employ encrypted information printed on a mailpiece. The postage value for a mailpiece may be encrypted together with other data to generate a digital token. A digital token is encrypted information that authenticates the information imprinted on a mailpiece including postal value. Examples of systems for generating and using digital tokens are described in U.S. Pat. No. 4,757,537 for SYSTEM FOR DETECTING UNACCOUNTED FOR PRINTING IN A VALUE PRINTING SYSTEM; U.S. Pat. No. 4,831,555 for UNSECURED POSTAGE APPLYING SYSTEM; U.S. Pat. No. 4,775,246 for SYSTEM FOR DETECTING UNACCOUNTED FOR PRINTING IN A VALUE PRINTING SYSTEM; U.S. Pat. No. 4,873,645 for SECURE POSTAGE DISPENSING SYSTEM; and, U.S. Pat. No. 4,725,718 for POSTAGE AND MAILING INFORMATION APPLYING SYSTEM. The entire disclosure of these five patents is hereby incorporated by reference.
As a result of the digital token incorporating encrypted value, such as postage value, altering the printed information in a Postal Revenue Block is detectable by standard verification procedures.
It has been recognized that to underpay postage, an attempt may be made to interfere with the rating process (as opposed to the resulting printed postage value). Systems have been developed to protect against such attempts by the use of hash values and encrypted hash values of various rating parameters and rate tables such as is disclosed in U.S. patent application Ser. No. 133,398 filed Oct. 8, 1993, for POSTAL RATING SYSTEM WITH VERIFIABLE INTEGRITY by Leon A. Pintsov, Richard A. Connell, Ronald P. Sansone, and Alfred C. Schmidt, and assigned to Pitney Bowes Inc.
In U.S. Pat. No. 4,873,645 for SECURE POSTAGE DISPENSING SYSTEM and U.S. Pat. No. 4,725,718 for POSTAGE AND MAILING INFORMATION APPLYING SYSTEM, as well as published French Patent Application 90 01284 (Publication No. 2 657 985 for PROCESS AND INSTALLATION FOR CONTROLLING THE COMPUTERIZED POSTAL METERING OF LETTERS; it has been disclosed that addressee information can be beneficially utilized as part of the encryption process to provide enhanced security against counterfeiting of the printed digital token since the encrypted information is unique to each address.